1. Field of the Invention
The present invention relates to a binder composition for electrode, a slurry for electrode containing the binder composition, and an electrode, a secondary battery, and others prepared by using the same.
2. Description of the Related Art
Devices reusable after recharging, for example secondary batteries such as lithium-ion secondary battery, nickel metal-hydride secondary battery, and nickel cadmium secondary battery and capacitors such as electric double-layer capacitor, have been used recently in electronic devices.
These secondary batteries and capacitors generally contain electrodes, a separator, and an electrolyte solution containing electrolytes. The electrodes are prepared as a mixture layer by coating and drying an electrode material slurry containing an electrode active material dispersed in a solvent containing a resin binder dissolved therein on an electrode current collector.
Polyvinylidene fluoride (hereinafter, referred to as PVDF), which has been frequently used industrially as a resin binder for lithium-ion secondary battery electrodes, cannot satisfy the requirements for high-performance batteries at the level demanded recently.
For example when PVDF is used as a binder, as disclosed in Patent Document 1, a nitrogen-containing organic solvent, for example an amide such as N-methylpyrrolidone (hereinafter, NMP) or a urea, is used as the solvent used in production of the mixture layer. However, the nitrogen-containing organic solvent such as NMP should be recovered, because release to the environment of the solvent vapor formed during the drying step causes an environmental problem.
Accordingly, proposed was use of an aqueous binder as the resin binder. For example, Patent Document 2 discloses a negative-electrode mixture paste prepared by dispersing a carbon material (as negative-electrode active material) and an aqueous mixture of an aqueous emulsion of acrylic copolymer and carboxymethylcellulose (as binder) in a solvent water.
However, conventional aqueous binders have been used mainly on negative electrode plates. They had a problem that they were less suited for coating on positive electrode plates, particularly because of insufficient dispersibility of the coating slurry in the electrode plate-producing process, and did not give batteries with sufficient performance.
Particularly recently, demand for improvement in performance of batteries lead to modification of electrode active substances, and there also exists currently a need for improvement in performance of the binder.